Recently, chargeable/rechargeable secondary batteries have been widely used as an energy source for wireless mobile devices. Also, the secondary battery has attracted considerable attention as a power source for electric vehicles (EVs), hybrid electric vehicles (HEVs), and plug-in hybrid electric vehicles (plug-in HEVs) which have been developed to solve problems, such as air pollution, caused by existing gasoline and diesel vehicles using fossil fuel. Such secondary batteries have been prepared in the form that an electrode assembly and an electrolyte solution are put in a battery case.
Electrode assemblies are classified into a stack type, a folding type, a stack-folding type, and a jelly-roll type. The stack or stack-folding type electrode assemblies have a structure obtained by interposing separators between multiple cathode units and multiple anode units, followed by sequentially laminating.
Meanwhile, the jelly-roll type electrode assemblies have a structure obtained by interposing a separator between a sheet type cathode having an active material applied on a current collector and a sheet type anode having an active material applied on a current collector, followed by winding, the cathode and the anode being prepared in advance. The unit electrode such as a cathode or an anode is prepared through the processes such as notching an electrode current collector at an interval of the unit electrode, applying an electrode slurry, applying a coating agent and so on. In such an overall processes for preparing of a battery, a sheet of an electrode is repeatedly subject to (re)winding. As used herein, the term ‘sheet’ is the generic term indicating both of current collectors having an active material applied thereon, and current collectors having no active material applied thereon. In this case, the part of an electrode to be first fed to (re)winding rolls is a fore part of a current collector. Referring to FIG. 1, the fore part of a current collector corresponds to an uncoated region 2a where an electrode active material layer is not formed thereon and more specifically the width direction end (W) of the uncoated region first begins to be fed to (re)winding rolls. Especially, a cathode current collector 2 is generally made of an aluminum foil, which may cause curling of the fore part during (re)winding due to its low tension of the current collector. When the fore part of an electrode is subject to curling, the biased movement of the electrode occurs and the electrode assembly fails to be laminated in the predetermined position, which may cause contact of the uncoated region of a cathode with an anode active material, contact of the uncoated region of an anode with a cathode active material or contact of the uncoated region of the cathode with the uncoated region of the anode, thereby causing an internal short-circuit.